The present invention relates to a magnetometer that may be sensitive to very small magnetic fluctuations in the presence of a much larger static field, and in particular to a magnetometer that measures precession of gas atoms in a way that the dephasing effects between gas atoms are reduced.
Atoms such as the alkali metals have a net spin which possesses a magnetic moment. Accordingly, if such atoms can be polarized and stimulated into precession, the frequency of precession can be used to precisely measure a magnetic field free from other influences. In this way, a precision magnetometer may be constructed.
The ability of alkali gas atoms to measure magnetic field is often limited by interactions between the alkali gas atoms (spin-exchange relaxation) themselves which cause de-phasing of the precessing alkali gas atoms. These interactions can be reduced, by eliminating any environmental magnetic field other than the field being measured (for example the Earth's magnetic field), for example by using nulling coils energized to produce a canceling countervailing magnetic field. Such magnetometers are termed “spin exchange relaxation-free (SERF) magnetometers.
Nulling the external magnetic field can be difficult and must be extremely precise to obtain the benefits of increased sensitivity of the alkali gas atoms.